Inspired by the construction of cMERA [1]}, a continuous version of the MERA tensor network,  [2]}, [3]} proposed the so-called surface/state correspondence as a more concrete mechanism of the holographic principle. In principle, this duality can be applied to any spacetime described by Einstein's gravity, even those without timelike boundaries. Surface/state correspondence (or SS duality) refers to the duality between a codimension two convex surface \(\Sigma \)  in the holographic bulk spacetime and a quantum state described by a density matrix \(\rho (\Sigma )\) , which is defined on the Hilbert space of the quantum theory dual to the Einstein's gravity.
